This invention relates to computer memory devices, and more particularly to means for protecting the integrity of electronically recorded data from the effects of ionizing radiation.
It is well known that a nuclear event generates effects felt far beyond the immediate area of the explosion. Electronic data storage systems are vulnerable to destruction from shock and thermal effects which would destroy data by physical destruction or disabling of the system. A data processing system sufficiently distant from a nuclear event to avoid physical destruction or impairment, nonetheless may experience damage from nuclear radiation. More particularly, a brief but powerful gamma ray pulse, known as prompt gamma, is emitted during the event and propagates outwardly at a speed near that of light. An electromagnetic pulse (EMP) is emitted as well. Neutrons also are emitted at the time of the explosion, but travel outwardly at much slower velocities. Peripheral areas thus receive gamma ray and EMP components first, followed by a high intensity fast neutron pulse. These pulses can destroy the memories of computer systems, for example by writing over previously recorded data, massive system overloading, or introduction of spurious signals into the memory. Internal computer memories, as well as peripheral memory devices such as disk drives, tape drives, and the like, are subject to this risk.
The need to protect data processing systems and other equipment from radiation has lead to the development of protective shields or covers to surround such equipment. For example, U.S. Pat. No. 4,556,757 (Oberbach) discloses a protective cover against radiation including a plastic carrier foil and a thin metal layer steamed onto the carrier foil and connected to ground potential. The carrier foil and metal layer are disposed between two plastic protective foils. A magnetic shield for charged particles is disclosed in U.S. Pat. No. 3,800,158 (Grosbard). The shield is constructed of magnetized elements which can be shaped as truncated pyramids, with one magnetic pole at the top of each pyramid and the other magnetic pole at the base. On a much larger scale, thick walls or partitions of lead can be employed to protect structure interiors against radiation.
Such shielding usually is inconvenient or impractical. Techniques are known for the "radiation hardening" of semiconductor chips and other forms of circuitry utilized in computers and in data storage devices. These techniques can be prohibitively expensive, however, costing hundreds of thousands of dollars for the complete radiation protection of a single disk drive.
Accordingly, signal handling and radiation detection techniques have been developed for the purpose of protecting the data stored in systems which are not totally radiation hardened. For example, U.S. Pat. No. 4,413,327 (Sabo et al) is directed to a computer system with an internal computer memory and two redundant storage units. The redundant units are alternatively addressed and updated in rapid alternating succession such that even during data recording operations the redundant units contain substantially the same information. Should a nuclear event occur while information is being written into one of the redundant storage units, the other unit remains isolated and therefore unaffected. When the high radiation of the event has ceased, the previously isolated memory is located and information from this memory loaded back into the computer's internal memory. The system includes a radiation detector for activating the interrupt and restoring circuits. While perhaps satisfactory under certain circumstances, this type of system increases the cost of data processing by at least a doubling the memory, as well as at least doubling the time required to gain access to memory in operations involving memory.
Therefore, it is an object of the present invention to provide a means to secure magnetically recorded data against the effects of nuclear radiation, without requiring radiation shielding or memory redundancy.
Another object of the invention is to provide a system for electronically recording information in which signals enabling recording can not be provided to memory once a nuclear or other high radiation event is detected.
Another object is to provide a data processing system in which a write enabling signal is delayed in its transmission to memory for a sufficient length of time to enable the detection of radiation above an accepted maximum level, as well as a disassociation of memory from the source of the write enable signal.
Yet another object is to provide a reliable and inexpensive means for securing previously stored magnetic data against alteration due to the electromagnetic pulse of a nuclear event.